VOL. XXXI.J PHILOSOPHICAL TRANSACTIONS, 507 



where it went to, after 28 vibrations. Taking out the water, I filled the trough 

 with mercury, the length of the pendulum, point of suspension and all other 

 things remaining as before : then letting go the ball in the mercury from the 

 same place whence it was let down when the trough was full of water, which 

 was marked by a string stretched across to prevent mistakes, after one whole 

 vibration, it came very little short of the same mark as it had come to in water 

 after 14 vibrations; and when it vibrated twice in mercury, it came to the same 

 place it had done after between 26 and 28 vibrations in water ; and this it did 

 exactly several times. 



Afterwards filling an upright copper pipe, of 4 inches diameter, with mer- 

 cury, to the height of 3 feet 10 inches, and suspending the golden ball in it 

 by a short string about an inch long, so as to have the ball just immersed 

 under the middle of the surface of the mercury; I caused it to be let down 

 suddenly, and observing how long it was in falling down to the bottom of the 

 tube, I found that the experiment was disturbed by the ball's striking against 

 the sides of the tube, which retarded the fall of the ball, and the more so the 

 oftener the ball struck : when the ball was least retarded, by not striking at 

 all, it was only 2± seconds in falling, which must be taken as the true time of 

 the fall of the ball through 46 inches of quicksilver. 



I also repeated the other experiments, making the golden pendulum 39.2 

 inches long, from the point of suspension to the centre of the ball, so as to 

 make it vibrate but once in a second, and then I found that it would vibrate 5 

 or 6 times in the mercury before the vibrations became so small as not to be 

 observed; and then the first vibration in the mercury ended very near where 

 the 14th in water had done; the second in mercury ended where the 27th in 

 water had done; and observing the third vibration in mercury, it ended exactly 

 at the mark where the 40th in water ended; and this was observed by several 

 persons as well as myself. The specific gravity of the mercury was, by trial, 

 found to be to water, as 13.44 to 1. As to the golden ball, which had varnish 

 and cement on it to keep the mercury from sinking into it, I found it to weigh 

 as follows, viz. in mercury 498 grains, in water 2424 grains, but in air 2577 

 grains. 



An Account of the Poison fVood Tree,* in New England. By the Hon. 

 Paul Dudley, F.R.S. N° 367, p. 145. 



^ The poison-wood-tree grows only in swamps, or low wet grounds, and is 



P something like a small ash, but more like a sumach, and therefore is by some 



* Rhus Vernix. Lin. 

 3 T 2 



